REPORT ON THE ANNELIDA. 
107 
strength from above downward {op. cit., pi. xv. fig. 4, one from the middle of the 
latter series). 
The proboscis forms a laterally compressed tube occupying the middle line of the 
anterior third of the animal. The mouth leads by a wide muscular gullet into this 
chamber. When extruded there are nine papillae superiorly, and nine inferiorly. Four 
short teeth guard the aperture. 
Externally the organ is invested by a transparent finely fibrous layer, which, after 
reaching half way backward on each side, converges to a muscular sli23 which is inserted 
into the middle of the posterior boss. Such a slip would ]3ull on the latter, probably in 
connection with the passage of a bolus. The whole canal is marked by evident trans- 
verse striae, caused by intersecting fibrous bands which enclose the vertical muscular fibres 
as it were with a loose parallel network, and which run continuously round the organ, 
intersected, however, at each lateral region by a line of the same nature running from 
front to back. These transverse bands are highly elastic, the fibres adhering together much 
more closely than the vertical fibres forming the main mass of the proboscis. This adhe- 
sion appears to be due to the granular sarcolemma. The function of this peculiar arrange- 
ment seems to be analogous to that of the reticulated layer in the Nernertean jDroboscis. 
In transverse section the proboscis shows externally the well-marked fibrous 
investment, which is densest at the two poles ,- then a series of radiate fibres which 
make uj) the bulk of the organ, and pass from without inward to the thin basement- 
layer beneath. These elastic fibres, as ordinarily seen, are parallel, and readily separated 
from each other. They are also smooth throughout, when isolated. In mass, however, 
they often present a peculiar wavy ap]3earance, a feature most marked externally. 
Cu’cular fibres occur here and there externally in the sections, so that they would 
ap 2 >ear to be present in most forms, though much more largely developed in some than 
others. The cap or external investment of each pole is formed of a layer differentiated 
from the rest. Externally is a coat of elastic tissue, then a stratum of thick 
zig-zag and probably elastic fibres which in thin transverse sections are continuous 
from side to side. In dilatation of the proboscis this elastic coat will probably be 
quite straight ; in the ordinary position in retraction it assumes a zig-zag condition. 
Beneath the basement-layer just mentioned is a considerable glandular and fibrous 
covering, apparently the homologue of the hypoderm. It is composed for the most 
part of fan-shaped groups of fibres spreading from a granular and glandular base toward 
the innermost coat of the organ. This forms a small conical fold, projecting inward, 
at each pole. The inner layer is firm, chitinous, and translucent. 
The ventral area is large and well defined, and the nerve-cords are rounded or ovoid. 
The hypodermic area is somewhat spindle-shaped, beginning by a narrow end under each 
longitudinal ventral muscle, and assuming considerable depth in the median line. The 
cuticle is of moderate thickness. 
